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92 CHAPTER 8. SPECIAL SITUATIONS IN X-PLANE
altitudes are way outside of normal human conception, so our ability to “hand-fly” these approaches
is next to nil.
During the first one hundred NASA Shuttle missions, the craft was hand-flown for the entire
re-entry only once, by a former Marine pilot who was ready for the ultimate risk and challenge.
In contrast, users flying the Space Shuttle in X-Plane will have to complete the entire mission by
flying by hand.
8.4.1 Walkthrough
To open the Space Shuttle for a re-entry flight into the atmosphere, go to the Aircraft menu and
select Aircraft & Situations. In the window that opens, click the Space Shuttle: Full Re-entry
button. X-Plane will load the craft at around 450,000 feet, in space, coming down at a speed of
Mach 20. Control will be limited in space (the craft is operating off of small reaction jets on the
Orbiter, set up as “puffers” in Plane-Maker), but once the shuttle hits atmosphere, there will be
some air for the flight controls to get a grip on and the craft will actually be able to be controlled.
The ship will first hit air at about 400,000 feet, but it will be so thin that it will have almost no
effect.
The airspeed indicator at this point will read around zero—interesting, since the craft is actually
moving at over 17,000 mph. The reason for this is that the airspeed indicator works based on how
much air is hitting it, just like the wings of the Orbiter do. In space, of course, that’s very little. The
indicated airspeed will build gradually as the craft descends. Under these conditions, even though
the Shuttle is actually slowing down, the airspeed indicator will rise as it descends into thicker air
that puts more pressure on the airspeed indicator. This oddity of the airspeed indicator, though,
is useful, since the air is also putting more pressure on the wings. This means you should get some
help with your research paper and the airspeed indicator is really measuring how much force the
wings can put out, which is really what a pilot is interested in here.
Restated, the airspeed indicator indicates the craft’s true airspeed times the square root of the
air density. It indicates lower speeds in thin air, but the wings put out less lift in thin air as well, so
the airspeed indicator works very well to tell the pilot how much lift can be put out by the wings.
If the airspeed indicator reads more than about 250 knots, the wings have enough air to generate
the lift to carry the aircraft. If the airspeed indicator is showing less than about 250 knots, then
the wings do not have enough air hitting them to lift the Shuttle, so it is still more or less coasting
in the thin upper atmosphere, where the air is too thin to do much for controlling flight.
As the airspeed indicator on the HUD gradually starts to indicate a value (as the aircraft
descends into thicker air), it means the craft is starting to ease down into the atmosphere at 15,000
mph like a sunburned baby trying to ease into a boiling-hot Jacuzzi—very carefully and very slowly.
Remember, if the craft was going 15,000 mph in the thick air of sea level, it would break up into
a million pieces in a microsecond. The only reason it survives at 15,000 mph up here is the air is
so thin that it has almost no impact on the ship. Again, the airspeed indicator tells how much the
air is really impacting the craft; 250 knots is a “comfortable” amount. The trick is to get the craft
moving much slower than 15,000 mph by the time it gets down to the thick air of sea level—and
to have it doing so at Edwards Air Force Base. This is what the re-entry is for, to dissipate speed
while descending so that the Orbiter is never going too fast for the thickness of the air that it is in.
It should only descend into the thicker air once it has lost some speed in the thinner air up higher.
The whole thing should be a smooth process wherein the ship doesn’t get rammed into thick, heavy
air at too high a speed.
Now, as the Orbiter begins to touch the outer molecules of the Earth’s atmosphere, you will
notice a slight ability to fly the ship as some air begins to pass over the wings. At the same time,